Catalytic hydrogenation of carbonized coal vapors



United States Patent 3,231,486 CATALYTlC HYDROGENATION 0F CARBONIZEDCOAL VAPORS Richard C. Perry, Charleston, and Charles W. Alhright,

South Charleston, W. Va., assignors to Union Carbide Corporation, acorporation of New York No Drawing. Filed Dec. 16, 1960, Ser. No. 76,113

3 Claims. (Cl. 2088) This invention relates to the stabilization of tarvapors resulting from thermal treatment of carbonaceous materials. Moreparticularly, this invention relates to the stabilization of vaporsproduced by low temperature coal carbonization processes so as to formlow molecular weight tar products.

A number of low temperatures coal carbonization processes have beendeveloped in the past. These processes comprise in general heating coalat a temperature of from about 400 C. to about 700 C. and recovering theresulting products: char, gas and tars. In many of these processes thecarbonization of the coal is conducted in a fluidized bed, withdrawingthe char from the bed, and condensing the vapors that form to recoverthe carbonization tar. Quite often the fiuidizing gas is air, althoughnitrogen, steam and hydrogen have also been used. Such processes havenot been extensively used in this country because the resulting productsare not of sufiicient value to make the processes economically feasible.The main product of these processes, amounting to about 70 to 75 weightpercent of the coal carbonized, is a char containing 15 to 20 percent ofvolatile material. At present, this char can be used as a solid fuel.But the worth of the unit heating value of the char is approximately thesame as the coal charged. About 6 to 7 weight percent of the coalcarbonized appears as Water, while another 6 to 7 weight percent of thecoal forms a gaseous product, which can be used as a fuel, and which hasa worth per unit heating value, at something greater than that of theoriginal coal. The remaining product, amounting to about 12 to 15 weightpercent of the coal carbonized, is a low temperature tar which basicallyhas the value of a liquid fuel oil. Because the fuel worth of theproducts is not much greater than that of the coal charged, lowtemperature carbonization processes have rarely been employed.

Various attempts have been made to upgrade the products of lowtemperature coal carbonization processes. Many of these attempts havecentered on the low temperature tar, because it is known to contain manypotentially valuable compounds, such as phenolic compounds, which can beused to manufacture phenolformaldehyde resins. Processing of the tar isdifficult, however, because it is heat sensitive, decomposes readily,and polymerizes easily due to its reactivity. Efforts atrevaporizationof the tar have not been satisfactory because much of the tar is a heavyasphalt that will not vaporize. It is believed that certain oxygenatedmaterials present in the tars, such as indenols, dihydroxy phenols,ethers and the like, that are easily polymen'zabl'e and are subject toattack by atmospheric oxygen, polymerize in the tar upon condensation,and tie up many of the reactive compounds present in the tar, therebyforming the asphalt.

Secondary treatments of the tar to enable recovery of the variouscompounds present in the'tar have not, to date, been particularlysuccessful. For example, liquid phase or mixed phase hydrogenation ofthe tar, using a fixed bed catalyst, is complicated by the shortcatalyst life normally encountered in such operations. Such shortcatalyst life requires expensive and time consuming shutdowns of theprocess for regeneration or renewal of the catalyst.

We have found that the amount of tar residue or asphalt obtained uponcondensation of the low temperature tar vapors can be materiallyreduced, in some cases to less than percent of the low temperature tarproduced,

and the quantity of low molecular weight oils correspondingly increasedif the vapors from the carbonization are stabilized by subjecting themto a mild catalytic hydrogenation treatment prior to their condensation.By operating in this way we effect the removal, in the vapor phase, ofthe unsaturated and reactive groups contained by the compounds resultingfrom the carbonizatiou, making a more stable, lower molecular weight tarwhich is more amenable to separation. In addition, by operating inaccordance with our invention, lower pressures can be employed than inthe hydrogenation processes which have been employed for the treatmentof the tars prior to our invention. Furthermore, the uncondensed gasrecovered from our process has been upgraded and has a substantiallyhigher heating value than the gases obtained from conventionalcarbonization processes.

The process of our invention essentially comprises stabilizing the tarvapors resulting from the carbonization of carbonaceous material bysubjecting said vapors to a catalytic hydrogenation prior to allowingsuch vapors to condense.

The process of this invention may be carried out with coals of allranks, including anthracite, bituminous, sub bituminous, and ligniticcoals and any other carbonaceous material which, upon carbonization,yields oxygenated compounds which readily polymerize upon condensation.

Catalysts that can be used in the process of this invention are thoseknown as hydrogen-treating catalysts. Such catalysts have been used inthe past for desu'lfurization', denitrification, deoxygenation, andhydrogenation of petroleum feed stocks. These catalysts, as commerciallyobtained, usually comprise oxides or sulfides of metals such as cobalt,molybdenum, nickel, zinc, chromium, and tungsten on a suitable supportmaterial. Tyical catalysts of this type are the cobalt molybdatecatalysts, which cornprise cobalt and molybdenum oxides on a suitablesupport. These catalysts contain, in general, from about 1.0 to about8.1 weight percent of cobalt and from about 5 to about 17 weight percentof molybdenum, based upon the total catalyst weight, the weight ratio ofmolybdenum to cobalt being, in general, from about 1.621. to about4.8:1.

These catalysts may also contain other'metal oxides, suchas nickel oxideand sodium oxide, the metal being present in an amount up to about 0.5Weight percent of the total catalyst Weight or they may contain onlycobalt oxide or molybdenum oxide alone.

Sulfide catalysts that are employed for desulfurization, deoxygenation,denitrification or hydrogenation processes are usually either nickelsulfide or a mixture of nickel and tungsten sulfides. Such catalysts maybe on a support material but are often used without a support material.A typical catalyst of the latter type is one prepared by thecoprecipitation of nickel and tungsten as the metals, followed by atreatment with hydrogen sulfide to convert the metals to the sulfides,giving a final composition having about 40 weight percent of tungstenand about 25 weight percent nickel.

Suitable support materials are bauxite, alumina, fullers earth andmontmorillonite. ally employed support material.

A particularly preferred catalyst for use in the process of the instantinvention comprises about 0.5 weight percent of nickel, about 1.0 weightpercent of cobalt and about 8.3 weight percent of molybdenum: based onthe total catalyst weight, onan alumina support, said metals beingpresent as their oxides.

The catalysts described above are reduced before the use in the processof the invention by beating them in a hydrogen atmosphere at atemperature of from about 350 C. to about 400 C. and a pressure of aboutone atmosphere for from about 4 hours to about 12 hours.

Patented Jan. 25, 1966 Alumina is the most gener The carbonizationreaction can be conducted in any manner known to the alt, such as byusing fixed beds, moving beds and fluidized beds of the carbonaceousmaterial.

The preferred carbonization process is that employing a fluidized bed ofthe material to be carbonized. When the process of this invention isemployed in conjunction with sucha carbonization process, the hydrogenused in the catalytic treatment can'be employed as the fluidizing gas,thus taking advantage of whatever hydrogenation of char occurs duringcarbonization.

When the carbonization is conducted in a fluidized bed, the charge, onheating, should not tend to agglomerate or form a coke residue on thewalls of the carbonizer. Such behavior can be avoided by including inthe charge a nonagglomerating material, such as a lignitic orsub-bituminous coal, whenever the carbonaceous feed has agglomeratingtendencies, whereby a non-agglomerating mixture is formed. Anothermethod of avoiding agglomeration of the feed is to subject the feed to apre-oxidation step in ways known in the art, or by the addition ofnon-agglomerating agents. Provision should be made to minimize carryover of solid particles to the catalyst bed.

The fluidizing gas is preferably preheated prior to being mixed with thecarbonaceous material to be carbonized to fromabout 300 C. to about 700C. and more preferably to about 400 C. Such preheating is not necessary,however, and the carbonization can be conducted without it.

The catalytic hydrogenation of this invention can be conducted athydrogen pressures of at least 200 p.s.i.g. This ability to stabilizethe coal tars from the carbonization at such low pressures is one of themajor advantages of the instant process over those previously employedto treat coal carbonization tars. But the process of our invention isnot limited to low pressures and can be applied after such processes asdry coal hydrogenation at about 3000 p.s.i.g. The higher pressuresresult in higher tar yields and accordingly higher yields of the lowmolecular weight oils produced by our process. It is preferred, however,to conduct the catalytic. hydrogenation at pressures of from about 200p.s.i.g. to about 3000 p.s.i.g., with pressures of from about 300p.s.i.g. to about 1000 p.s.i.g. being particularly preferred.

The coal carbonization can be carried out at temperatures of from about450 C. to about 600 C.,and preferably at temperatures of from about 500to 550 degrees centigrade.

It is essential to this invention that the vapors from the carbonizationare not permitted to condense prior to the catalytic hydrogenation.Therefore, temperatures of from about 400 C. to about475 C., andpreferably from about 420" C. to about 430 0., should be maintained inthe catalyst bed as well as in the vapor line from the carbonizationreactor to the catalyst bed.

In a particularly preferred embodiment of the process of this invention,particulate carbonaceous material is mixed with hydrogen that has beenpreheated to about 400 C. at a pressure of about 400 p.s.i.g.,and ispassed to a carbonization zone where the carbonaceous material is heatedto about 500550 C. The resulting char, or

solid product, is removed from the carbonization-zone and the vaporsfrom the carbonization are passed over a catalyst containing 0.5 part byweight of nickel, 1.0 part by weight of cobalt and 8.3 parts by weightof molybdenum, on an alumina support at a temperature of about 425 C.and a pressure of about 400 p.s.i.g. The vapors are then condensed.Uncondensed gases are mixed with fresh hydrogen and are recycled to thecarbonization.

The following examples are illustrative of the process of thisinvention.

EXAMPLE 1 The apparatus employed comprised two batch coal feed hoppersconnected in parallel, each hopper-having a capacity of 3500 grams ofcoal, suflicient for 6 to 10 hours of operation; Process gas from agas-cylinder manifold was preheated to about 400 C. and was then mixedwith the coal fed continuously from the hopper. The resulting gassolidsmixture was conducted to the base of the carbonizer where the coal wasfluidized at such a rate that the char retention time within the reactorwas about 15 minutes. The carbonizer consisted of an 8-inch long tubehaving an inside diameter of 1 inch and fitted with an expanded head.The carbonizer was equipped with two electrical heating circuits.Thermocouples located 1, 4, 7, and 12 inches from the bottom of thecarbonizer were installed in a Ai-inch outside diameter thermowellplaced axially in the center of the reactor. The lower threethermocouples were in the fluidized bed while the upper thermocouple wasin the vapor space above the bed. An electrically heated char overflowline at the top of the fluidized bed conducted the char to a charreceiver. An electrically heated vapor line conducted the vapors fromthe top of the carbonizer to the catalyst tube, a metal tube 32 incheshigh and having an inside diameter of 1 inch. Heat was supplied to thetube through 3 independent electrical circuits. A A-inch outsidediameter thermowell was installed along the axis of the catalyst tubeand contained 5 thermocouples equally spaced along the length of thetube. Ceramic saddles, used as packing for non-catalytic runs, werereplaced with a commercially obtainable catalyst comprising 8.3 weightpercent of molybdenum, 1.0 weight percent of cobalt and 0.5 weightpercent of nickel, said metals being present as their oxides on analumina support for the catalytic run. The catalyst was reduced inhydrogen prior to use.

The recovery system consisted of a steam cooled pri mary condenser, awater cooled secondary condenser, a ceramic saddle-packed acetonescrubbing tube to'assure removal of the tar fog, and a final watercooled condenser placed in series. A portion of the uncondensed gas wasvented to the atmosphere and the remainder of this gas was recycled foruse as the fluidizing gas. Suflicient hydrogen was added to the recycledgas to maintain a hydrogen concentration in the gas stream of at least60 percent, after which the gas stream was reheated to 400 C., mixedwith powdered coal and conducted to the carbonizer.

The coal employed was Elkol coal, a commercial, strip-mined Wyoming coalclassified as a sub-bituminous B coal. The coal was pulverized to pass a40 mesh screen and then oven dried at C. in a nitrogen att mosphereprior to use. The analysis of the feed is summarized in Table I below:

TABLE I Proximate analysis (dry basis): Weight percent Volatile matter43.3 0.5

Ash 2.8 -0.3

Fixed carbon 539:1.0

Ultimate analysis (moisture, ash free basis):

0 (by difference) 173:0,5

A weighed batch of the dried coal was charged to the feed hopper, theunit was pressurized and the gas flow established. The coal feed fromone of the hoppers was set at the desired rate and the coal was mixedwith process gas, either nitrogen or hydrogen, that was preheated toapproximately 400 C. Since char retention time in the reactor was 15minutes, the pre-run was continued for 15 minutes after equilibrium wasestablished in the system. At the end of the pre-run period the liquidand char receivers were drained, the coal fiow from the second hopperwas started and the run was started.

TABLE II [Operating conditions] Run Number 1 2 *3 Flnidizing Gas N2 H2H2 Pressure, p.s.i.g 400 400 400 Average Hydrogen partial pressure,p.s.i.g 341 290 Carbonization Temp., C 515 515 515 Catalyst Temp, C 435Time of Run, hr 8.42 Coal Feed Rate, glILfllI 4G9 Catalyst SpaceVelocity, lb. tar/ lb. catalyst/hr 0. 42 Linear Gas Velocity (inCarbonizer), itJsec 0.1 0.5 0.5 Hydrogen Circulation Rate, SCFH Nil 10080 Catalytic Run.

PRODUCTS, WEIGHT PERCENT [Moisture, ash free basis] Run Number 1 2 3Char 75. 3 72. 2 Water 8. 7 11.7 Tar 8. 2 7.7. Gas 7. 3 8. 8 HydrogenReacted 0. 3 1. Unaccounted for 0. 0 0.8 0. 6

After completion of a run, the carbonizer and catalyst bed were cooled.The run char was removed from the char receiver and weighed. The liquidproduct (tar) from the four condensers was drained into a common vessel.

The char obtained by the above-described procedure is typical of thoseobtained from low temperature carbonization processes.

The gas recycled to the carbonizer was analyzed and these analyses areshown in Table III below:

hour. The mixture was cooled to room temperature and the hexane extractwas poured off, leaving insoluble asphalt as a residue. The hexaneextract was distilled in a small laboratory packed column to a kettletemperature of 200 C., removing the n-hexane, which was shown by gaschromatographic analysis to contain a negligible amount or" oil. The oilremaining in the kettle was comb'ned with the earlier-obtained oil fromthe dewatering step. The yields of tar, asphalt and oil obtained in each10 run are summarized in Table IV below.

TABLE IV Run Number From Table IV it can be seen that the process ofthis invention results in an increase in the amount of oil from 66pounds per ton of the coal charged for the noncatalytic,nitrogen-fluidized run (Run 1) to about 120 pounds per ton of coalcharged for the process of this invention (Run 3). There is acorresponding reduction in the amount of asphalt produced from 58 poundsper ton of coal for the nitrogen runs to about 30 pounds per ton of coalfor the catalytic hydrogenation runs.

The reduction in the amount of asphalt resulting from the coalcarbonization effected by our process is believed TABLE III Run Number 12 3 Yield:

Lb./ton of coal 224 142 170 CF/ton of coal 3, 085 1, 810 2, 550

Analysis (H and N2 free basis), Volume Percent Com orent:

do as. 3 32. 2

Heating Value, B

From Table III it can be seen that the heating value of the gas isupgraded by the process of this invention, which upgrading is dueprimarily to the increase in the ratio of- CO to CO of from 0.77 for thenitrogen run (Run 1) to a value of 2.35 for the catalytic hydrogenationrun (Run 3).

The liquid product from the condensers, a mixture of tar, water andacetone, was distilled in a small laboratory packed column to a headtemperature of 70 C. at a 6:1 reflux ratio. The distillate consisted ofacetone with negligible amounts of oil, as determined by gaschromatographic analysis. The distillation was then continued to a headtemperature of 110 C. (maximum kettle temperature of 200? C.). Thedistillate contained light oil-and water, which were separated bydecantation. The tar residue remainIng in the kettle was extracted with4 parts by weight of n-hexane to 1 part by weight of residue by warmingon a steam bath with stirring for 1 to be caused mainly by the reductionof compounds containing hetero atoms, such as nitrogen, sulfur andoxygen, in the tar. The amounts of hetero atoms found in the tar fromthe various runs are set forth in Table V below:

TABLE v [Hetero atoms, wt. percent of tar] Run Number 1 2 3 Oxygen 10. 69; 3' 5. 7 Nitrogen. 1. 0 0. 9 0. 9 Sulfur 0. 7 0; 6 0. 4

From Table V it can be seen that the process of this invention reducesthe amount of hetero atoms present in the tar from 12.3 weight percentfor the run conducted in nitrogen (Run 1) to 7 weight percent for thecatalytic hydrogen-fluidized process (Run 3).

The oil obtained from each run was distilled and the fraction boiling ata temperature of from 110 C. to 260 C. was recovered. This fractionamounted to about 44.5 volume percent of the oil recovered from Run 1,about 42.5 volume percent of theoil recoveredfrom Run 2 and about 46.6percent of the oil recovered from run 3.

These fractions were then extracted to recover the phenols contained inthe oil. The yields are shown in Table VI From Table VI it can be seenthat the process of this invention substantially increases the amount oflow molecular Weight phenols that can be recovered from the tarsproduced by coal carbonization processes and particularly increases theamount of phenols, cresols and xylenols (C C phenols) that can berecovered.

EXAMPLE 2 Employing the apparatus'and operating procedures of Example 1,Lake de Smet Coal, a Wyoming coal classified as a sub-bituminous C coal,was carbonized at a hydrogen partial pressure of about 900 p.s.i. Theanalysis of the feed is summarized in Table VII below:

TABLE VII.-LAKE DE SMET COAL ANALYSIS Proximate analysis (dry basis):Weight percent The operating conditions and product yields of thecarbonization are shown in Table VIII below:

TABLE VIIIl-LAKE DE SMET COAL [Operating Conditions] Run Number 1 2 3Fluidization Gas N2 H H2 Pressure, p.s.i.g 200 1, 000 1, 000 Avg. H2Partial Pressure, p.s. .g nil 900 920 Carbonization Temp, C. 515 525 515Catalyst Temperature, C 42 Time of Run, hrs 5. 58 6. 42 7. 58 Goal FeedRate, gm./hr 560 486 422 Catalyst Space Velocity, lb. tar/lb.

catalyst/hr 0. 82 Linear Gas Velocity (in carbonizer),

itu/sec. O. 23 0. 33 t). 31 Hydrogen Circulation Rate, SCFH nil 165 150*Catalytic Run.

[Products, weight percent (moisture, ash tree basis)] Run Number 1 2 3Char 68. 6 42. 43. 1 Water 9. 7 18. 2 21. Tar. 12.5 28. 2 23. 1 Gas 9. 313. 4' 14. 4 Hydrogen Reacted -2.0 2.2 Unaccounted for- 0. 0 0. 2 0. 1

The gas yields and analyses of the gas products from each run are shownin Table 1X below:

TABLE IX.GAS YIELD AND ANALYSIS Run Number 1 2 3 Yield:

Lb./Ton of Coal 186 270 288 CF/Ton of Coal 3, 780 4, 520 4, 860

[Analysis (H2 and N2 irce basis), volume percent] From Table IX it canbe seen that the process of this invention increased the heating valueof the gas from 340 B.t.u. per cubic foot for the nitrogen run and 803B.t.u. per cubic foot of the n n-catalytic hydr 8 to 918 B.t.u. percubic foot for the catalytic hydrogenation of this invention. The yieldsof tar, oil and asphalt are set forth in Table X below:

TABLE X.TAR YIELDS Run NumbeL 1 2 3 Yields, Lb. per Ton of Coal Yield s,percent of tar Oil 49 44 83 Asphalt. 51 56 17 Percent of Tar Distillablm75. 0 S8. 5 Percent of Tar Boiling 110260 C 31. 0

From Table X it can be seen that the yield of oil was increased both asto absolute yield and as to percent of the tar. Furthermore, the percentof tar distillable at reduced pressures (about 5 mm. of Hg) beforedecomposition sets in, increased'from percent for the noncatalytichydrogenation to 88.5 percent for the catalytic hydrogenation.

The elemental analyses of the tars resulting from the hydrogenations areset forth in Table XI below:

TABLE XL-ELEMENTAL ANALYSIS OF TABS FROM LAKE DE SMET COAL From Table XIit can be seen that the catalytic hydrogenation reduces the amount ofhetero atoms present in the tar, thus causing a reduction in the amountof asphalt formed. The most striking reduction was that of nitrogen from0.9 percent to only 0.3 percent.

What is claimed is:

1. A process which comprises mixing a particulate coal with hydrogen gasat pressures of from about 200 p.s.i. to about 3000 p.s.i., feeding theresulting gas-solids mixture to a carbonization zone wherein the solidsare present in the form of a fluidized bed, heating the gas-solidsmixture in said carbonization zone at temperatures of from about 450 C.to about 600 C., withdrawing the vapors from said heating from saidcarbonization zone and passing them over a hydrogenation catalyst in asubstantially separate hydrogenation zone at a temperature of from about400 C. to about 475 C. and a pressure of from about 200 p.s.i. to about3000 p.s.i. prior to the condensation of said vapors.

2. A process which comprises mixing a particulate coal with hydrogen gasat pressures of from about 300 p.s.i. to about 1000 p.s.i., heating theresulting gas-solids mixture in a carbonization zone at temperatures offrom about 500 C. to about 550 C., withdrawing the vapors from saidheating from said carbonization zone and passing them over ahydrogenation catalyst in a substantially separate hydrogenation zone ata temperature of from about 400 C. to about 475 C. and a pressure offrom about 300 p.s.i. to about 1000 p.s.i. prior to the condensation ofsaid vapors.

3. The process of claim 2 wherein the hydrogenation catalyst is aluminaimpregnated with 0.5 weight percent nickel, 1.0 weight percent cobaltand 8.3 weight percent molybdenum, based on the Weight of alumina, saidmetals being present as their oxides, which metal oxides have beensubsequently reduced.

5 References Cited by the Examiner UNITED STATES PATENTS 5/1934 Grimm eta1 2088 7/ 1937 Pier et a1 208-10 8/1938 Winkler 208-10 10 4/ 1939 Pieret a1 208-10 10 6/1945 Thomas 20810 3/ 1949 Storch et a1 208-10 8/ 1952Storch et al 208-10 5/ 1953 Kalbach 208-11 10/ 1963 Huntington 208-8FOREIGN PATENTS 2/ 1929 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

1. A PROCESS WHICH COMPRISES MIXING A PARTICULATE COAL WITH HYDROGEN GASAT PRESSURES OF FROM ABOUT 200 P.S.I. TO ABOUT 3000 P.S.I., FEEDING THERESULTING GAS-SOLIDS MIXTURE TO A CARBONIZATION ZONE WHEREIN THE SOLIDSARE PRESENT IN THE FORM OF A FLUIDIZED BED, HEATING THE GAS-SOLIDSMIXTURE IN SAID CARBONIZATION ZONE AT TEMPERATURES OF FROM ABOUT 450*C.TO ABOUT 600*C., WITHDRAWING THE VAPORS FROM SAID HEATING FROM SAIDCARBONIZATION ZONE AND PASSING THEM OVER A HYDROGENATION CATALYST IN ASUBSTANTIALLY SEPARATE HYDROGENATION ZONE AT A TEMPERATURE OF FROM ABOUT400*C. TO ABOUT 475*C. AND A PRESSURE OF FROM ABOUT 200 P.S.I. TO ABOUT3000 P.S.I. TO THE CONDENSATION OF SAID VAPORS.